Cutaneous reflexes will be studied in normal and in extra (transplanted) limbs of Xenopus Laevis. These experiments are performed in spinal curarized animals using electrophysiological techniques. Research in progress suggests that the reflexes in the extra limb are substantially the same as those in normal limb even when the extra limb is innervated by cells from thoracic segments. These phenomena will be investigated in greater detail and the cellular basis for these normal extra limb reflexes will be investigated using single cell recordings. The major question to be asked is whether the extra limb is truly innervated by thoracic neurons as indicated by the gross anatomy (suggesting modulation) or whether these limbs are innervated by lumbar neurons via thoracic roots (suggesting out-growth specificity). The convergence from the periphery of the normal and extra limb onto spinal neurons will also be studied. Intracellular recordings from motoneurons in anesthetized cats will be used to study the projection from each of several Ia afferent fibers onto the same motoneuron. The properties of the unitary excitatory post synaptic potentials (EPSP's) from each afferent will be used to account for quantitative aspects of the monosynaptic reflex in terms of amount of transmitter release per presynaptic impulse and the location of the terminal on the motoneuron's soma and dendrites.